1. Field of the Invention
This invention relates to an electric motor vehicle, such as an electrical locomotive or an electric vehicle (EV), equipped with batteries and a vehicle propelling motor-generator.
2. Description on the Related Art
Propelling an electric motor vehicle with a vehicle propelling motor requires an electric power source which can supply sufficient driving power to the motor. A pure EV uses a secondary battery, sometimes a lead battery, as an electric power source. Furthermore, a so-called hybrid vehicle may use, together with a secondary battery, a secondary electric power source, such as an engine-driven-generator, a solar cell, or a fuel cell (Japanese Patent Laid-Open Publication No. Hei 5-199609). In any case, a relatively high power-supply voltage of, for example, DC 250 V is generally required to drive a high output vehicle propelling motor. In order to achieve such a high voltage, batteries connected in series can be used.
To use these batteries connected in series as the secondary battery, operations such as an equalizing charge and a refreshing discharge are necessary to prevent an unequal status (that is, unequal electrode status or unequal electromotive forces), which shorten battery life, between these batteries. The equalizing charge stated above is known as an operation in which serially-connected batteries are charged to a slightly excessive charging level; the refreshing discharge is an operation in which almost all electricity is discharged from serially-connected batteries. Both operations equalize battery electrode states by introducing extremely high or low state of charge (SOC). In connection with an equalizing charge or a refreshing discharge, conventional electric motor vehicles have a problem that a manual connecting operation of a charger or a discharger to the secondary battery is required.
This problem is especially serious for hybrid vehicles. Hybrid vehicles can be classified into series hybrid vehicles, parallel hybrid vehicles, or their combinations or variations. A series hybrid vehicle can charge its secondary battery by electric output from other on-board electric power sources such as an engine-driven-generator; a parallel hybrid vehicle can charge its secondary battery by electric output from a generator coupling an engine and driving wheels. That is, since the various types of hybrid vehicles can charge secondary batteries with on-board components, exclusive apparatuses such as a charger and a discharger and manual operations thereof are not necessary to propel these vehicles.
Nevertheless, because equalizing charge and refreshing discharge are necessary, hybrid vehicles must be equipped with a charger and a discharger and must be used in the environment in which the infrastructure such as charging and discharging facilities are available along roads or in garages. Since the equalizing charge and the refreshing discharge are not performed frequently, this equipment and the infrastructure is very expensive. Therefore, in addition to the above troublesome operations, there exists a problem of high implementation costs such as building cost of charging and discharging facilities etc. and necessity to provide infrastructures including a number of garages with charging and discharging facilities etc.